1. Field
The disclosure relates to a vehicle and, in particular, to a technique of diagnosing presence or absence of an abnormality of a current sensor that is mounted in a vehicle.
2. Description of Related Art
In general, a current sensor is connected in series to a current path that connects a battery and a power control unit mounted in an electric vehicle. Charging and discharging of the battery are controlled based on a detection value of this current sensor.
Such an abnormality that the detection value of the current sensor is at least offset by a specified amount possibly occurs. An abnormality diagnosis of whether such an abnormality has occurred can be made based on the detection value (so-called an offset value) of the current sensor that is acquired in a state where a current does not flow through the current path. For example, an abnormality detector for a current sensor disclosed in Japanese Patent Application Publication No. 2007-99033 (JP 2007-99033 A) determines an abnormality of the current sensor based on a detection value of the current sensor in a state where an electric power supply to an electrical load is blocked by a blocking means (specifically, a relay) in the case where an ignition switch is turned off.
There is a high possibility that an abnormality of the current sensor caused by a reason such as deterioration by aging is permanent. Meanwhile, the inventors have paid attention to a fact that a temporal abnormality also possibly occurs to the current sensor.
As an example of the temporal abnormality, a case of condensation on the current sensor is raised. In detail, an amount of water vapor that can be contained in the air is reduced as a temperature is lowered. Accordingly, for example, in the case where an ignition-off operation is performed under such an environment that an atmospheric temperature (more specifically, a peripheral temperature of the current sensor) is low, water droplets are possibly generated on a connector that is provided in a wiring path for transmitting an output signal from the current sensor. Alternatively, there is a case where the water droplets are generated on a processing board for the output signal from the current sensor. In such a case, the offset value of the current sensor indicates an abnormal value due to an increase of a leakage current caused by the water droplets or the like, and it is possibly diagnosed that there is the abnormality of the current sensor.
However, the condensation is possibly eliminated when the atmospheric temperature is raised along with a lapse of time. In such a case, the offset value of the current sensor returns to a normal value. As a result, such a diagnosis result that the abnormality has occurred to the current sensor possibly becomes an error.
Such a phenomenon possibly occurs in a situation as will be described below. For example, the condensation possibly occurs on the current sensor when the atmospheric temperature is low, such as in the early morning. In the case where the ignition-off operation is performed after a short-time travel in this state, a current value is acquired by using the current sensor in a state where the condensation thereon remains, and the current value is stored in a memory. Because the ignition-off operation has already been performed, a diagnosis of whether there is the abnormality of the current sensor is not made at this time point. Thereafter, for example, in the case where an ignition-on operation is performed after the atmospheric temperature is raised in the daytime, there is a possibility that the condensation on the current sensor has already been eliminated. In the case where the current value that is acquired in the early morning is read from the memory and an abnormality diagnosis is made based on the value in this state, it is possibly diagnosed that there is the abnormality of the current sensor.